Not applicable.
1. Field of the Invention
This invention relates to pumps such as compressors and vacuum pumps, and in particular to a housing for a pump.
2. Discussion of the Prior Art
Reciprocating piston or diaphragm pumps typically have a metal housing, for example, a cast aluminum alloy, in which bearings are mounted which journal the shaft which drives the pump. A metal housing is needed, particularly for larger pumps, to withstand the forces of driving the piston or diaphragm and containing the pressure exerted in the compression chamber of the pump.
A rotary electric motor is usually used to drive these pumps and the motor requires cooling. In one such pump, the motor is provided between two housings, each of which is separate from the other and houses one compression chamber. The shaft of the motor is a through shaft so that each end of the shaft mounts one of the pistons or diaphragms that work to vary the volume of the compression chamber in the housing at the corresponding end of the shaft. Further out from where the piston or diaphragm is mounted, a rotary fan blade is mounted to each end of the shaft to draw a flow of cooling air into the housing at that end and blow it onto the rotor and stator coils of the motor.
For cooling efficiency, it is desirable to make the part of the housing in which the rotary fan blade is mounted circular and just slightly larger than the diameter of the fan blade. The clearance between the tips of the fan blades and the interior housing surface should be as small as possible because, if not, the air drawn into the housing by the fan blades will simply blow back out past the tips of the blade, and not be directed over the coils of the motor. For applications in which the pump is contained inside of a separate enclosure, it may be permissible to leave the end of the housing at which the fan blade is mounted open. However, if the pump is going to be exposed or sold as a stand-alone product, the end of the housing must be closed with a cover which permits air to be drawn into the housing, but prevents the insertion of larger objects or fingers. This cover, typically called a fan guard, should not deleteriously affect the operation of the fan nor add to the lateral size or detract from the appearance of the fan.
The invention provides a fan guard which easily attaches to the housing, without requiring any special machining of the housing, does not increase the internal clearance for the fan and does not add to the lateral size of the housing or detract from its appearance. The fan guard is perforated so as to permit the inflow of air to the housing past it, and has peripheral tabs which extend into the housing in a direction parallel to the axis of the shaft. The tabs have a crescent-shaped profile, and similarly shaped recesses are formed in the housing. The crescent-shaped recesses of the housing have holes formed in them. Each tab of the fan guard has an ear which snaps into the hole in the corresponding recess to hold the fan guard in place over the end of the housing.
In a preferred form, the recesses and holes are cast-in features of the housing. The holes which are formed in the recesses preferably have a horizontal axis to permit them to be formed during the casting process, since inserts in the die move in this direction, which is perpendicular to the parting line of the casting. As a consequence, the axes of all the holes in the recesses are parallel to one another. Each ear also has an axis, which is the major direction it extends from the tab, and this axis of the ear generally corresponds to the axis of the hole, so that the ear axis is parallel to the hole axis when the ear is received in the hole. A ramped surface is preferably provided on the distal end of the ear, to flex the tab inwardly upon insertion of the fan guard in the end of the housing, and the proximate end of the ear is squared off so that the ear snaps into the hole and the near side of the hole is caught by the proximal end of the ear when the snap-in fan guard tabs are inserted into the end of the housing.
The crescent-shaped tabs, which are also referred to herein as D-shaped, are preferably somewhat smaller than the similarly shaped recesses in the housing so that the inward surface of the tabs approximates a continuation of the inner surface of the housing so as not to interfere with the fan blades or require an excessive clearance between the tips of the fan blades and the interior of the housing. It is preferred that the inner surface of the tab be somewhat recessed within the crescent-shaped recess so that if the ear is not fully engaged in the hole, or if the fan guard is removed with the fan turning, the tabs do not flex so far inwardly as to interfere with the tips of the blade.
Any number oftabs and corresponding recesses around the periphery of the crank case portion of the housing may be provided. In a preferred form, four tabs and corresponding recesses are provided. The tabs and recesses are provided with two on each side of the housing and the two on each side spaced as far apart as possible, with one toward the top of the crank case portion and the other toward the bottom of the crank case portion on each side. Spacing the holes apart vertically helps provide a secure fixation.
The fan guard will generally be round, but it is desirable to provide at least one feature which extends radially from the fan guard or otherwise serves to position the fan guard angularly in the proper location relative to the housing. This feature may fit into a similarly shaped opening in the compression chamber portion of the housing without adding to the width or height of the compressor.
It is also noted that if the ears and holes have their axes horizontal, and the housing recesses are arranged symmetrically on opposite sides of a vertical axis, the holes and ears on opposite sides of the housing at the top of the housing will be along one horizontal axis and at the bottom of the housing will be along a different horizontal axis. Thus, the tabs at the top press against the housing opposite to one another and the tabs at the bottom press against the housing opposite to one another to hold the fan guard in position.